Poly(arylene thioethers) (hereinafter abbreviated as "PATEs") represented by poly(phenylene sulfide) (hereinafter abbreviated as "PPS") are polymers having predominant recurring units of arylene thioether represented by the formula, --Ar--S-- wherein --Ar-- means an arylene group, and are used in a wide variety of application fields because they are excellent in heat resistance, flame retardance, chemical resistance, mechanical properties and the like.
Since PPS is generally poor in impact strength, it has been proposed to blend a polyamide with PPS into a resin composition improved in impact resistance (Japanese Patent Publication No. 1422/1984). However, PPS is insufficient in compatibility with the polyamide, so that the mere blending of PPS with the polyamide results in a molded or formed product poor in surface profile and also insufficient in effect to improve mechanical properties.
In Macromol. Chem., Vol. 191, 815-828 (1990), there is disclosed a process for the production of a block copolymer containing PPS blocks and polyamide blocks, in which a polyamide is polymerized in the presence of a telechelic PPS containing functional groups such as carboxyl group on its both terminals. According to this process, a polymer having good mechanical properties may possibly be obtained. The process however involves a drawback that its operation, treatment and the like are complicated.
Japanese Patent Application Laid-Open No. 231968/1991 discloses a resin composition composed of a carboxyl-containing PPS, a hydrogenated styrene-butadiene block copolymer and a polyamide. The invention described in this publication intends to introduce carboxyl groups into PPS to give PPS reactivity to an amino group on the terminal of the polyamide, thereby solving the problem that PPS is insufficient in compatibility with the polyamide. According to this publication, as the carboxyl-containing PPS, there is used a polymer obtained by upon the reaction of an alkali metal sulfide with a dihalobenzene in an organic amide to produce a PPS, causing a carboxyl-containing aromatic halide such as 2,4-dichlorobenzoic acid or p-chlorobenzoic acid to coexist in the reaction system.
However, such a carboxyl-containing PPS tends to undergo decarboxylation upon its melt blending, or molding or forming and processing at an elevated temperature, whereby its carboxyl groups are decomposed. As a result, it is considered that the effect of the functional groups introduced into the polymer is impaired. In addition, The conventionally-known process for the production of the carboxyl-containing PPS can provide a polymer only in the form of powder and hence involves a problem that the handling properties of the polymer are deteriorated.
Japanese Patent Application Laid-Open No. 283763/1990 discloses a resin composition obtained by mixing and kneading a modified PPS, which has been obtained by reacting a carboxylic anhydride to a poly(phenylene sulfide) resin prepared by the conventionally-known process, and a thermoplastic resin such as a polyamide resin. More specifically, this modification reaction is carried out by a process wherein PPS powder is dry-blended with the carboxylic anhydride, and the resultant blend is then melted and kneaded in an extruder controlled at 290.degree.-310.degree. C. and then extruded through the extruder into pellets. In the modified PPS obtained by this process, however, sufficiently strong chemical bonding does not occur between the carboxylic anhydride and PPS. Therefore, the resin composition composed of the modified PPS and polyamide is also hard to acquire satisfactory mechanical properties.
On the other hand, the present assignee previously filed a patent application as to a process for the production of a granular PATE containing carboxyl groups, in which an alkali metal sulfide, a dihalogenated aromatic compound and a dihalogenated aromatic carboxylic acid are subjected to a polymerization reaction in the presence of an alkaline earth metal compound in a polar solvent containing water (EP 494518; CA 2,056,332). In addition, a patent application as to a blend of the carboxyl-containing PATE and a polyamide was also filed (Japanese Patent Application Laid-Open No. 51532/1993). The introduction of carboxyl groups into PATE makes it possible to improve the compatibility of PATE with polyamide. Such a polymer however involves a drawback that the carboxyl groups introduced therein are insufficient in heat stability, and the resulting blend may hence be hard in some cases to acquire good mechanical properties under thermally severe processing conditions.